1. Field of the Invention
The present invention relates to a hexagonal type barium titanate powder, a producing method thereof and a dielectric composition including the hexagonal type barium titanate as a main component, more precisely, relates to a dielectric ceramic composition which shows desired characteristics (for example, extremely high specific permittivity) and is preferable to produce a dielectric layer for electronic components such as a ceramic capacitor and the like which can maintain a sufficient reliability. Also, the present invention relates to an electronic component having dielectric layer composed of the dielectric ceramic composition.
2. Description of the Related Art
In recent years, electric apparatus and electronic apparatus have been rapidly downsized and high performance. Along with that, it has been required to improve various characteristics (specific permittivity, temperature characteristics and the like) of electronic components used for such apparatuses with maintaining sufficient reliability. A ceramic capacitor as one example of electronic components is not exception.
As for dielectric material of such capacitor, particularly for dielectric material having high specific permittivity, tetragonal type barium titanate which includes tetragonal barium titanate as a main component, and cubic type partially has been used. By the way, in recent years, for improving a capacitance, it has been studied to make a dielectric layer thinner. In order to realize to make the dielectric layer thinner, smaller particle diameter of the dielectric particle is preferable. However, when atomizing the tetragonal type barium titanate powder as mentioned above, there was a problem that the specific permittivity is reduced.
As for a material having high specific permittivity, hexagonal barium titanate has been studied. Although the hexagonal barium titanate has essentially low specific permittivity than the tetragonal type barium titanate, in Japanese Patent No. 3941871, it has been suggested that the specific permittivity can be improved extremely by introducing oxygen vacancy to hexagonal barium titanate single crystal.
However, the present inventors have progressed to study based on the teaching in the above mentioned Japanese Patent No. 3941871, it has been found that an insulation property is reduced even though the specific permittivity is improved by introducing the oxygen vacancy. Therefore, when the hexagonal barium titanate having improved specific permittivity by introducing oxygen vacancy is used for element, there is a risk to reduce lifetime of the element and the like.
Also, in a crystal structure of the barium titanate, hexagonal structure is a metastable phase, normally, it can be exist only at 1460° C. or higher. Therefore, in order to obtain the hexagonal barium titanate in a room temperature, it is necessary to cool rapidly from the high temperature of 1460° C. or higher.
In this case, a specific surface area of the obtained hexagonal barium titanate becomes 1 m2/g or less because of the rapid cooling from the high temperature, thus a coarse powder is only obtained. When producing electronic components with thinner dielectric layer by using such coarse powder, there is a problem that it cannot maintain the sufficient reliability, because the powder fails to adapt to the thinner dielectric layer.
By the way, as for a producing method of the hexagonal barium titanate, for example, Non-Patent Literature 1 discloses that BaCO3, TiO2 and Mn3O4 are used as starting raw materials and are heat-treated. By this means, a transformation temperature to hexagonal phase can be lowered, hexagonal barium titanate in which Mn is solid-soluted is obtained by a heat treatment at a temperature lower than 1460° C.
However, specific surface area of the hexagonal barium titanate obtained in the Non-Patent Document 1 is approximately 1.6 m2/g, thus it is insufficient for applying a thinner dielectric layer in the electronic components even though using this hexagonal barium titanate powder.
Non-Patent Literature 1 is “Properties of Hexagonal Ba(Ti1-xMnx)O3 Ceramics: Effects of Sintering Temperature and Mn Content”, Japanese Journal of Applied Physics, 2007 Vol. 46 No. 5A 2978-2983.